Determination of optimal diameters for nanowires

ABSTRACT

Methods of optimizing the diameters of nanowire photodiode light sensors. The method includes comparing the response of nanowire photodiode pixels having predetermined diameters with standard spectral response curves and determining the difference between the spectral response of the photodiode pixels and the standard spectral response curves. Also included are nanowire photodiode light sensors with optimized nanowire diameters and methods of scene reconstruction.

FIELD OF INVENTION

The embodiments relate to nanowire devices, more particularly, tomanufacturing nanowire image sensors.

BACKGROUND

An image sensor has a large number of sensor elements (pixels),generally greater than 1 million, in a Cartesian (square) grid.Conventional color image sensors are fabricated with colored filtersarranged in a Bayer configuration. An Example of a convention Bayerconfiguration is illustrated in FIG. 6. The color scheme includes red,green, and blue filters (RGB). The Bayer filter pattern is 50% green,25% red and 25% blue, hence is also referred to GRGB or otherpermutation such as RGGB. Twice as many green elements as red or blueare used to mimic the human eye's greater resolving power with greenlight. Since each pixel is filtered to record only one of three colors,the data from each pixel cannot fully determine color on its own. Toobtain a full-color image, various demosaicing algorithms can be used tointerpolate a set of complete red, green, and blue values for each pointin the sensed scene.

Indeed, to obtain the full color image of the scene, data from all threecolor filters is required. Because data from all three color filters isrequired and each row of filters only has two types of color filter, atleast two rows of pixels must be used to reproduce the scene using aBayer configuration. This, in turn, has implications on the performanceof image processing. Conventional digital image processors process onerow at a time. Therefore, at least one row of sensor data must be heldin a buffer while data from the next row is processed. In this manner,red, green, and blue data for each point in the image can be processed,however, it comes at the cost of processing speed.

One challenge of a designer of color image sensors is to consistentlyalign the color response of the sensor pixels to the response curve ofthe human eye. Filter-based color sensors are device dependent. That is,different devices detect or reproduce different RGB values. The RGBvalues typically vary from manufacturer to manufacturer based on themanufacturer's selection of dye or phosphor used to make their filters.Further, filter degradation over time may even lead to variations in theRGB values over time in the same device.

The layers of a typical sensor are listed in Table I and shown in FIG.1.

TABLE I Typical Layer Description Thickness (μm) 15 OVERCOAT 2.00 14MICRO LENS 0.773 13 SPACER 1.40 12 COLOR FILTER 1.20 11 PLANARIZATION1.40 10 PASS3 0.600 9 PASS2 0.150 8 PASS1 1.00 7 IMD5B 0.350 6 METAL331.18 5 IMD2B 0.200 4 METAL2 21.18 3 IMD1B 0.200 2 METAL1 1.18 1 ILD0.750

In Table I, typically the first layer on a silicon substrate is the ILDlayer and the topmost layer is the overcoat. In Table I, ILD refers to ainter-level dielectric layer, METAL1, METAL2 and METAL3 refer todifferent metal layers, IMD1B, IMD2B and IMD5B refer to differentinter-metal dielectric layers which are spacer layers, PASS1, PASS2 andPASS3 refer to different passivation layers (typically dielectriclayers).

The total thickness of the layers above the silicon substrate of theimage sensor is the stack height (s) of the image sensor and is the sumof the thickness of the individual layers. In the example of Table I,the sum of the thickness of the individual layers is typically about11.6 micrometers (μm).

The space above the photosensitive element of a pixel must betransparent to light to allow incident light from a full color scene toimpinge on the photosensitive element located in the silicon substrate.Consequently, no metal layers are routed across the photosensitiveelement of a pixel, leaving the layers directly above the photosensitiveelement clear.

The pixel pitch to stack height ratio (p/s) determines the cone of light(F number) that can be accepted by the pixel and conveyed to thephotosensitive element on the silicon. As pixels become smaller and thestack height increases, this number decreases, thereby lowering theefficiency of the pixel.

More importantly, an increased stack height with greater number of metallayers obscure the light from being transmitted through the stack toreach the photosensitive element, in particular of the rays that impingethe sensor element at an angle. One solution is to decrease the stackheight by a significant amount (i.e., >2 μm). However, this solution isdifficult to achieve in a standard CMOS process.

Another issue, which possibly is the one that most limits theperformance of the conventional image sensors, is that less than aboutone-third of the light impinging on the image sensor is transmitted tothe photosensitive element such as a photodiode. In the conventionalimage sensors, in order to distinguish the three components of light sothat the colors from a full color scene can be reproduced, two of thecomponents of light are filtered out for each pixel using a filter. Forexample, the red pixel has a filter that absorbs green and blue light,only allowing red light to pass to the sensor.

Other issues may also affect the efficiency of the pixel. For example,the difference in refractive index between the microlens 14 and theovercoat layer 15 will cause some of the incident photons to reflect offthe overcoat rather than be transmitted to the photosensitive element.Typically, the difference between the refractive indices of air (n=1.0)and a typical polymer (n=1.5) overcoat 15 is small, resulting in a smallreflective loss. Another, larger reflective loss, however, is generatedat the boundary between the inter-level dielectric layer 1 (n=1.5) andthe substrate 20 (n=4−5). This is due to the larger difference betweenthe refractive indices of the inter-level dielectric layer 1 (n=1.5) anda typical silicon substrate 20 (n=4−5). Another loss may occur due tothe incident light hitting the overcoat at too severe an angle and notbeing transmitted to the photosensitive element. Additionally, realdevices have a quantum efficiency less than 100%. That is, even whenphotons reach the photosensitive element, a finite number of them do notproduce a signal.

Another issue that plagues image sensors is crosstalk. Crosstalk is aphenomenon by which a signal transmitted in one pixel or channel of atransmission system creates an undesired effect in another pixel orchannel. For optical sensors, there are at least three types ofcrosstalk: (1) spatial optical crosstalk, (2) spectral crosstalk, and(3) electrical crosstalk. Spatial optical crosstalk occurs when thepixel size approaches the wavelength of visible light. Diffractioncauses a sharp increase in the amount of light that reaches adjacentphotodiodes rather than the desired photodiode. Spectral crosstalk iswhen light that should have been blocked by a color filter manages topass through the filter. Electrical crosstalk is when photo-generatedelectrons travel to adjacent pixels through the silicon substrate.

The development of nanoscale technology and in particular the ability toproduce nanowires has opened up possibilities of designing structuresand combining materials in ways not possible in planar technology. Onebasis for this development is that the material properties of a nanowiremakes it possible to overcome the requirement of placing a color filterson each photo diode of an image sensor and to significantly increase thecollection of all the light that impinges on the image sensor.

Nanowires of silicon can be grown on silicon without defects. In US20040075464 by Samuelson et al. a plurality of devices based on nanowirestructures are disclosed.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a cross sectional view of a conventional image sensor.

FIG. 2 shows a cross sectional view of an embodiment of an image sensor.

FIG. 3 shows a portion of an array of image sensors

FIG. 4 shows a schematic of a top view of a device containing imagesensors of the embodiments disclosed herein, each image sensor havingtwo outputs representing the complementary colors.

FIG. 5 is a plot of the Smith-Pokorny standard spectral response curves.

FIG. 6 is a schematic illustration of a conventional Bayer color scheme.

FIG. 7 illustrates a simulation of the absorption of a 60 nm wire and a80 nm wire.

FIG. 8 illustrates a simulation of the absorption the substrates of a 60nm wire and a 80 nm wire device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

This disclosure is drawn, inter alia, to methods, apparatus, systems,and devices related to an image sensor and nanowire pixels. Anembodiment relates to a method for optimizing the diameter of thenanowires of an image sensor. Another embodiment relates to a firstmethod of scene reconstruction by transforming digitized response froman array of nanowire photodiode devices by calculating the red, green,and blue color of the scene. Another embodiment relates to a secondmethod of scene reconstruction by transforming digitized response froman array of nanowire photodiode devices by calculating the luminance andchrominance of the scene. In the first scene reconstruction method, thescene is reconstructed by stepping across the array of nanowirephotodiode devices one photodiode at a time. In the second scenereconstruction method, the scene is reconstructed by stepping across thearray of nanowire photodiode devices two photodiodes at a time. Anotherembodiment relates to a device having at least two different pixels thatinclude nanowire photodiodes having nanowires with diameters optimizedto minimize the differences between the spectral response of the deviceand the human eye. The response of the human eye may be taken from astandard spectral response curve. Another embodiment relates to acomputer readable medium which is configured to simulate the spectralresponse of a nanowire photodiode and determine the error differencebetween the spectral response of a nanowire photodiode of apredetermined diameter and the human eye. The simulation may be used todetermine the optimal diameter of the nanowire in the nanowirephotodiode to minimize the difference between the nanowire photodiodeand the human eye.

An embodiment relates to a method of determining a diameter for ananowire for a nanowire device comprising providing a first nanowiredevice comprising at least a first pixel and a second pixel, wherein thefirst pixel comprises a first nanowire comprising a predeterminedmaterial and a predetermined diameter, the first pixel configured todetect a first predetermined color and a first complementary color ofthe first predetermined color, and the second pixel comprises a secondnanowire comprising a second predetermined material and a secondpredetermined diameter, the second pixel configured to detect a secondpredetermined color and a second complementary color of the secondpredetermined color, determining a first error difference between afirst predetermined color spectral response of the first predeterminedcolor of the first nanowire and one or more standard spectral responsecurves, determining a second error difference between a firstcomplimentary color spectral response of the first complementary colorof the first nanowire and one or more standard spectral response curves,determining a third error difference between a second predeterminedcolor spectral response of the second predetermined color of the secondnanowire and the one or more standard spectral response curves anddetermining a fourth error difference between a second complimentarycolor spectral response of the second complementary color of the secondnanowire and the one or more standard spectral response curves, anddetermining a total error difference from the first, second, third, andfourth error differences.

In one aspect of this embodiment, the method further comprisingproviding a plurality of additional nanowire devices, each of theadditional nanowire devices comprising at least an additional firstpixel and an additional second pixel, wherein each of the additionalfirst pixels comprises an additional first nanowire comprising the samepredetermined material as the first nanowire but having a differentdiameter from each of the other additional first nanowires and from thefirst nanowire and each of the additional second pixels comprise anadditional second nanowire comprising the same predetermined material asthe second nanowire but having a different diameter from each othersecond additional nanowires and from the second nanowire determining thetotal error differences between spectral responses of the plurality ofadditional nanowire devices and the one or more standard spectralresponse curves and determining the diameters of the nanowires of thenanowire device of the first nanowire device and the plurality ofadditional nanowire devices that produces the least error differencebetween the spectral responses with standard spectral response curves.

In another aspect of this embodiment, the standard spectral responsecurves are Smith-Pokorny eye response spectral curves. In anotheraspect, the standard spectral response curves are CIE standard observercurves. Preferably, the total least error difference is determined witha least squares analysis. In one aspect of the embodiment, the firstpixel is configured to detect blue and yellow and the second pixel isconfigured to detect cyan and red. In another aspect, the first pixel isconfigured to detect blue and yellow and the second pixel is configuredto detect cyan and red and determining the first, second, third, andfourth error differences between the spectral response of the spectralresponses of the first and second nanowires and the Smith-Pokorny eyeresponse spectral curves comprises determining the constants in thefollowing equations:Rsp˜Ayr*Ynw+Abr*Bnw+Arr*Rnw+Acr*Cnw,Gsp˜Ayg*Ynw+Abg*Bnw+Arg*Rnw+Acg*Cnw,Bsp−Ayb*Ynw+Abb*Bnw+Arb*Rnw+Acb*Cnw,where Rsp, Gsp, and Bsp are the Smith-Pokorny eye response spectralcurves, Ynw (yellow), Bnw (blue) and Rnw (red), and Cnw (cyan) are thespectral responses of the first and second nanowires, respectively, andAyr, Abr, Arr, Acr, Ayg, Abg, Arg, Acg, Ayb, Abb, Arb, and Acb areconstants.

In another aspect, the nanowire device comprises an optical pipecomprising a core and a cladding, wherein the core is configured totransmit light with wavelengths up to the predetermined color. In anaspect, the first nanowire has a diameter of approximately 60 nm and thesecond nanometer has a diameter of approximately 80 nm when the materialused for the construction of the nano wire is Si. In another aspect, themethod further comprises fabricating a sensor array having a pluralityof first and second pixels. In another aspect, the sensor arraycomprises rows and columns of alternating first and second pixels.

Another embodiment relates to a method of scene reconstructioncomprising receiving digitized responses of an array of nanowirephotodiode devices, the array comprising a alternating plurality offirst nanowire photodiode devices and second nanowire photodiodedevices, the first nanowire photodiode devices configured to detect afirst color and a first complementary color complementary to the firstcolor and the second nanowire photodiode devices configured to detect asecond color and a second complementary color complementary to thesecond color and transforming the digitized responses by stepping acrossa row of alternating first and second nanowire photodiode devices andsuccessively calculating the red, green, and blue scene color from apair of adjacent first and second nanowire photodiode devices, whereinstepping across the row is performed one nanowire photodiode device at atime. In aspect of the embodiment, transforming the digitized responsescomprises calculating the red, green, and blue scene color with thefollowing equations for a first yellow/blue nanowire photodiode deviceadjacent to a second red/cyan nanowire photodiode device:R1=Ayr*Y1+Abr*B1+Arr*R2+Acr*C2,G1=Ayg*Y1+Abg*B1+Arg*R2+Acg*C2,B1=Ayb*Y1+Abb*B1+Arb*R2+Acb*C2,where Y1, B1 and R2, C2, are spectral responses of the first yellow/bluenanowire photodiode device and the second red/cyan nanowire photodiodedevice, respectively, and Ayr, Abr, Arr, Acr, Ayg, Abg, Arg, Acg, Ayb,Abb, Arb, and Acb are constants.

In another aspect, transforming the digitized responses comprisescalculating the red, green, and blue scene color with the followingequations for a third yellow/blue nanowire photodiode device adjacent tothe second red/cyan nanowire photodiode device:R2=Ayr*Y3+Abr*B3+Arr*R2+Acr*C2,G2=Ayg*Y3+Abg*B3+Arg*R2+Acg*C2,B2=Ayb*Y3+Abb*B3+Arb*R2+Acb*C2,Where Y3, B3 and R2, C2 are spectral responses of the third yellow/bluenanowire photodiode device and the second red/cyan nanowire photodiodedevice, respectively, and Ayr, Abr, Arr, Acr, Ayg, Abg, Arg, Acg, Ayb,Abb, Arb, and Acb are constants.

Another embodiment relates to a method of scene reconstructioncomprising receiving digitized responses of an array of nanowirephotodiode devices, the array comprising an alternating plurality offirst nanowire photodiode devices and second nanowire photodiodedevices, the first nanowire photodiode devices configured to detect afirst color and a first complementary color complementary to the firstcolor and the second nanowire photodiode devices configured to detect asecond color and a second complementary color complementary to thesecond color and transforming the digitized responses by stepping acrossa row of alternating first and second nanowire photodiode devices andsuccessively calculating the luminance and chrominance of the scene froma pair of adjacent first and second nanowire photodiode devices, whereinstepping across a row is performed a pair of nanodiode devices at atime.

In one aspect of the embodiment, transforming the digitized responsescomprises calculating the luminance and chrominance of the scene withthe following equations for a first yellow/blue nanowire photodiodedevice adjacent to a first red/cyan nanowire photodiode device:Luminance1=Ly*Y1+Lb*B1Luminance2=Lr**R2+Lc*C2Chrominance1=Ayu*Y1+Abu*B1+Aru*R2+Acu*C2Chrominance2=Ayv*Y1+Abv*B1+Arv*R2+Acv*C2where Y1, B1 and R2, C2 are the spectral responses of the first andsecond nanowire photodiode devices, respectively, and Ly, Lb, Lr, Lc,Ayu, Ayv, Abu, Abv, Aru, Arv, Acu, and Acv are constants. Another aspectfurther comprises using a 4:2:2 subsampling in which the output pixeldata stream is arranged in luminance chrominance sequence such as:Luminance1, Chrominance1, Luminance2, Chrominance2, . . . .

Another embodiment relates to a device comprising at least a first pixeland a second pixel, wherein the first pixel comprises a first nanowirecomprising a predetermined material and a predetermined diameter, thefirst pixel configured to detect a first predetermined color and a firstcomplementary color of the first predetermined color and the secondpixel comprises a second nanowire comprising a second predeterminedmaterial and a second predetermined diameter, the second pixelconfigured to detect a second predetermined color and a secondcomplementary color of the second predetermined color, wherein the firstnanowire and the second nanowire have diameters which were determined toproduce the least total error difference between spectral responses ofthe first and second pixels with standard spectral response curves. Inone aspect, the device is an optical sensor. In another aspect, thestandard spectral response curves are Smith-Pokorny eye responsespectral curves. In another aspect, the standard spectral responsecurves are CIE standard observer curves. Preferably, the least totalerror difference is determined with a least squares analysis.

In one aspect of the embodiment, the first pixel comprises a first lightpipe comprising the first nanowire and a first cladding surrounding thefirst nanowire and the second pixel comprises a second light pipecomprising the second nanowire and a second cladding surrounding thefirst nanowire. In another aspect, the first pixel comprises a firstlight pipe comprising only first nanowire and a cavity surrounding thefirst nanowire and the second pixel comprises a second light pipecomprising the second nanowire and a second cavity surrounding the firstnanowire. In this aspect, the complementary colors are detected with aphotodiodes in the substrate of the first and second pixels. In anotheraspect, the first pixel further comprises a reflective surfacesurrounding the first light pipe and the second pixel further comprisesa reflective surface surrounding the second light pipe. In anotheraspect, the first pixel comprises a first substrate and a firstphotodiode in the first substrate, the second pixel comprises a secondsubstrate and a second photodiode in the second substrate. In anotheraspect, the first complementary color is detected by the firstphotodiode in the first substrate and the second complementary color isdetected by the second photodiode in the second substrate.

Another embodiment relates to a tangible computer readable mediumcomprising computer executable instructions for simulating a firstnanowire device comprising at least a first pixel and a second pixel,wherein the first pixel comprises a first nanowire comprising apredetermined material and a predetermined diameter, the first pixelconfigured to detect a first predetermined color and a firstcomplementary color of the first predetermined color and the secondpixel comprises a second nanowire comprising a second predeterminedmaterial and a second predetermined diameter, the second pixelconfigured to detect a second predetermined color and a secondcomplementary color of the second predetermined color and determiningthe error difference between a spectral response of the first pixel andthe second pixel with standard spectral response curves.

One aspect of the embodiment, the computer readable medium furthercomprises instructions for simulating a plurality of additional nanowiredevices, each of the additional nanowire devices comprising at least anadditional first pixel and an additional second pixel, wherein each ofthe additional first pixels comprises an additional first nanowirecomprising the same predetermined material as the first nanowire buthaving a different diameter from each of the other additional firstnanowires and from the first nanowire and each of the additional secondpixels comprise an additional second nanowire comprising the samepredetermined material as the second nanowire but having a differentdiameter from each other second additional nanowires and from the secondnanowire, determining the error difference between the spectralresponses of the plurality of additional nanowire devices and one ormore standard spectral response curves and determining the diameters ofthe nanowires of the nanowire device of the first nanowire device andthe plurality of additional nanowire devices that produces the leasttotal error difference between the spectral responses with standardspectral response curves. In another aspect, the least error differenceis determined with a least squares analysis.

A waveguide has a cutoff wavelength that is the lowest frequency thatthe waveguide can propagate. As a result, an ideal waveguide in the corewhose cutoff wavelength is at green will not propagate red light, and anideal waveguide in the core whose cutoff wavelength is at blue will notpropagate red and green light. Real waveguides, of course, will suffersome spectral crosstalk. That is, a real waveguide in the core whosecutoff wavelength is at green will propagate a small amount of red lightand an real waveguide in the core whose cutoff wavelength is at bluewill propagate a small amount of red and green light. In oneimplementation, a first pixel includes a blue waveguide embedded withina white waveguide, which could be in the cladding. A second pixelincludes a cyan (blue/green waveguide) embedded within a white waveguidecladding. Preferably, blue light remains in the blue waveguide core,while blue and/or green light remains in the cyan waveguide of thesecond core. Preferably the remainder of the light remains in the whitewaveguide in one or more the claddings.

An optical pipe is an element to confine and transmit an electromagneticradiation that impinges on the optical pipe. The optical pipe caninclude a core and a cladding.

A core and a cladding are complementary components of the optical pipeand are configured to separate wavelengths of an electromagneticradiation beam incident on the optical pipe at a selective wavelengththrough the core and cladding. An active element is any type of circuitcomponent with the ability to electrically control electron and/or holeflow (electricity controlling electricity or light, or vice versa).Components incapable of controlling current by means of anotherelectrical signal are called passive elements. Resistors, capacitors,inductors, transformers, and even diodes are all considered passiveelements. Active elements in embodiments disclosed herein include, butare not limited to, an active waveguide, transistors, silicon-controlledrectifiers (SCRs), light emitting diodes, and photodiodes. A waveguideis a system or material designed to confine and direct electromagneticradiation of selective wavelengths in a direction determined by itsphysical boundaries. Preferably, the selective wavelength is a functionof the diameter of the waveguide. An active waveguide is a waveguidethat has the ability to electrically control electron and/or hole flow(electricity controlling electricity or light, or vice versa). Thisability of the active waveguide, for example, is one reason why theactive waveguide could be considered to be “active” and within the genusof an active element.

An embodiment relates to methods to enhance the transmission of light tooptically active devices on an integrated circuit (IC). In someembodiments, the device is configured to resolve black and white orluminescence information contained in the electromagnetic radiation byappropriate combinations of energies of the electromagnetic radiationdetected in the core and the cladding.

In the embodiments disclosed herein, preferably, the core comprises awaveguide. Preferably, the active element is configured to be aphotodiode, a charge storage capacitor, or combinations thereof. Morepreferably, the core comprises a waveguide comprising a semiconductormaterial. The device could further comprise a passivation layer aroundthe waveguide in the core. The device could further comprise a metallayer around the waveguide in the core. The device could furthercomprise a metal layer around the passivation layer. Preferably, thedevice comprises no color or IR filter. The optical pipe may becircular, non-circular or conical. Preferably, the core has a core indexof refraction (n₁), and the cladding has a cladding index of refraction(n₂), wherein n₁>n₂ or n₁=n₂.

In some embodiments, the device could further comprise at least a pairof metal contacts with at least one of the metal contacts beingcontacted to the waveguide. Preferably, the optical pipe is configuredto separate wavelengths of an electromagnetic radiation beam incident onthe optical pipe at a selective wavelength through the core and thecladding without requiring a color or IR filter. Preferably, thewaveguide is configured to convert energy of the electromagneticradiation transmitted through the waveguide and to generate electronhole pairs (excitons). Preferably, the waveguide comprises a PINjunction that is configured to detect the excitons generated in thewaveguide.

In some embodiments, the device could further comprise an insulatorlayer around the waveguide in the core and a metal layer around theinsulator layer to form a capacitor that is configured to collect theexcitons generated in the waveguide and store charge. The could devicefurther comprise metal contacts that connect to the metal layer andwaveguide to control and detect the charge stored in the capacitor.Preferably, the cladding is configured to be a channel to transmit thewavelengths of the electromagnetic radiation beam that do not transmitthrough the core. Preferably, the cladding comprises a passivewaveguide.

In some embodiments, the device could further comprise a peripheralphotosensitive element, wherein the peripheral photosensitive element isoperably coupled to the cladding. Preferably, an electromagneticradiation beam receiving end of the optical pipe comprises a curvedsurface. Preferably, the peripheral photosensitive element is located onor within a substrate. Preferably, the core and the cladding are locatedon a substrate comprising an electronic circuit.

In some embodiments, the device could further comprise a lens structureor an optical coupler over the optical pipe, wherein the optical coupleris operably coupled to the optical pipe. Preferably, the optical couplercomprises a curved surface to channel the electromagnetic radiation intothe optical pipe.

In some embodiments, the device could further comprise a stacksurrounding the optical pipe, the stack comprising metallic layersembedded in dielectric layers, wherein the dielectric layers have alower refractive index than that of the cladding. Preferably, a surfaceof the stack comprises a reflective surface. Preferably, the corecomprises a first waveguide and the cladding comprises a secondwaveguide.

Other embodiments relate to a compound light detector comprising atleast two different devices, each device comprising a optical pipecomprising a core and a cladding, the optical pipe being configured toseparate wavelengths of an electromagnetic radiation beam incident onthe optical pipe at a selective wavelength through the core and thecladding, wherein the core is configured to be both a channel totransmit the wavelengths up to the selective wavelength and an activeelement to detect the wavelengths up to the selective wavelengthtransmitted through the core, and the compound light detector isconfigured to reconstruct a spectrum of wavelengths of theelectromagnetic radiation beam. Preferably, the core comprises a firstwaveguide having the selective wavelength such that electromagneticradiation of wavelengths beyond the selective wavelength transmitsthrough the cladding, further wherein the selective wavelength of thecore of each of the at least two different devices is different suchthat the at least two different devices separate the electromagneticradiation beam incident on the compound light detector at differentselective wavelengths. Preferably, the cladding comprises a secondwaveguide that permits electromagnetic radiation of wavelengths beyondthe selective wavelength to remains within the cladding and betransmitted to a peripheral photosensitive element. Preferably, across-sectional area of the cladding at an electromagnetic radiationbeam emitting end of the cladding is substantially equal to an area ofthe peripheral photosensitive element. The compound light detector couldfurther comprise a stack of metallic and non-metallic layers surroundingthe optical pipe.

Preferably, the compound light detector is configured to detect energiesof the electromagnetic radiation of four different ranges of wavelengthswherein the energies of the electromagnetic radiation of the fourdifferent ranges of wavelengths are combined to construct red, green andblue colors.

Other embodiments relate to a compound light detector comprising atleast a first device and a second device, wherein the first device isconfigured to provide a first separation of an electromagnetic radiationbeam incident on the optical pipe at a first selective wavelengthwithout any filter, the second device is configured to provide a secondseparation of the electromagnetic radiation beam incident on the opticalpipe at a second selective wavelength without any filter, the firstselective wavelength is different from the second selective wavelength,each of the first device and the second device comprises a core that isconfigured to be both a channel to transmit the wavelengths up to theselective wavelength and an active element to detect the wavelengths upto the selective wavelength transmitted through the core, and thecompound light detector is configured to reconstruct a spectrum ofwavelengths of the electromagnetic radiation beam. Preferably, the twodifferent devices comprise cores of different diameters. Preferably, thespectrum of wavelengths comprises wavelengths of visible light, IR orcombinations thereof. Preferably, the first device comprises a core of adifferent diameter than that of the second device and the spectrum ofwavelengths comprises wavelengths of visible light, IR or combinationsthereof.

Preferably, the first device comprises a first waveguide having thefirst selective wavelength such that electromagnetic radiation ofwavelength beyond the first selective wavelength will not be confined bythe first waveguide, wherein the second device comprises a secondwaveguide having the second selective wavelength such thatelectromagnetic radiation of wavelength beyond the second selectivewavelength will not be confined by the second waveguide, further whereinthe first selective wavelength is different from the second selectivewavelength. Preferably, the first device further comprises a firstwaveguide that permits electromagnetic radiation of wavelength ofgreater than the first selective wavelength to remains within the firstwaveguide and the second device further comprises a second waveguidethat permits electromagnetic radiation of wavelength of greater than thesecond selective wavelength to remains within the second waveguide.Preferably, each of the first and second devices comprises a claddingcomprising a photosensitive element. The compound light detector couldfurther comprise a stack of metallic and non-metallic layers surroundingthe first and second devices. Preferably, the first device comprises acore of a different diameter than that of the second device and thespectrum of wavelengths comprises wavelengths of visible light.Preferably, a plurality of light detectors are arranged on a squarelattice, an hexagonal lattice, or in a different lattice arrangement.

In yet other embodiments, the lens structure or the optical couplercomprises a first opening and a second opening with the first openingbeing larger than the second opening, and a connecting surface extendingbetween the first and second openings. Preferably, the connectingsurface comprises a reflective surface. In yet other embodiments, aplurality of light detectors are arranged on a regular tessellation.

In yet other embodiments, as shown in FIG. 2, a coupler that may takethe shape of a micro lens could be located on the optical pipe tocollect and guide the electromagnetic radiation into the optical pipe.As shown in FIG. 2, the optical pipe comprises of a nanowire core ofrefractive index n₁ surrounded by a cladding of refractive index n₂.

In the configuration of the optical pipe of FIG. 2, it is possible toeliminate pigmented color filters that absorb about ⅔ of the light thatimpinges on the image sensor. The core functions as an active waveguideand the cladding of the optical pipe could function as a passivewaveguide with a peripheral photosensitive element surrounding the coreto detect the electromagnetic radiation transmitted through the passivewaveguide of the cladding. Passive waveguides do not absorb light likecolor filters, but can be designed to selectively transmit selectedwavelengths. Preferably, the cross sectional area of the end of thecladding of the optical pipe adjacent to the peripheral photosensitiveelement in or on the substrate below the cladding is about the same sizeas the area of the peripheral photosensitive element.

A waveguide, whether passive or active, has a cutoff wavelength that isthe lowest frequency that the waveguide can propagate. The diameter ofthe semiconductor waveguide of the core serves as the control parameterfor the cutoff wavelength of the waveguide. In some embodiments, theoptical pipe could be circular in or cross section so as to function asa circular waveguide characterized by the following parameters: (1) thecore radius (R_(c)); (2) the core index of refraction (n₁); and (3) thecladding index of refraction (n₂). These parameters generally determinethe wavelength of light that can propagate through the waveguide. Awaveguide has a cutoff wavelength, λ_(ct). The portion of the incidentelectromagnetic radiation having wavelengths longer than the cutoffwavelength would not be confined with the core. As a result, an opticalpipe that functions as a waveguide whose cutoff wavelength is at greenwill not propagate red light though the core, and an optical pipe thatfunctions as a waveguide whose cutoff wavelength is at blue will notpropagate red and green light through the core.

In one implementation, a blue waveguide and a cyan (blue/green)waveguide could be embedded within white waveguides, which could be inthe cladding. Blue light could remain in the blue waveguide core, blueor green light could remain in the cyan (green/blue) waveguide ofanother core. The remainder of the light could remain in the whitewaveguides in one or more the claddings.

The core could also serve as a photodiode by absorbing the confinedlight and generating electron hole pairs (excitons). As a result, anactive waveguide in the core whose cutoff wavelength is at green willnot propagate red light but will also absorb the confined green lightand generate excitons.

Excitons so generated can be detected by using at least one of thefollowing two designs:

(1) A core is made up of a three layers, semiconductor, insulator andmetal thus forming a capacitor to collect the charge generated by thelight induced carriers. Contacts are made to the metal and to thesemiconductor to control and detect the stored charge. The core could beformed by growing a nanowire and depositing an insulator layer and ametal layer surrounding the nanowire.(2) A core having a PIN junction that induces a potential gradient inthe core wire. The PIN junction in the core could be formed by growing ananowire and doping the nanowire core while it is growing as a PINjunction and contacting it at the appropriate points using the variousmetal layers that are part of any device.

The photosensitive elements of the embodiments typically comprise aphotodiode, although not limited to only a photodiode. Typically, thephotodiode is doped to a concentration from about 1×10¹⁶ to about 1×10¹⁸dopant atoms per cubic centimeter, while using an appropriate dopant.

The layers 1-11 in FIG. 2 illustrate different stacking layers similarto layers 1-11 of FIG. 1. The stacking layers comprise dielectricmaterial-containing and metal-containing layers. The dielectricmaterials include as but not limited to oxides, nitrides and oxynitridesof silicon having a dielectric constant from about 4 to about 20,measured in vacuum. Also included, and also not limiting, are generallyhigher dielectric constant gate dielectric materials having a dielectricconstant from about 20 to at least about 100. These higher dielectricconstant dielectric materials may include, but are not limited tohafnium oxides, hafnium silicates, titanium oxides, barium-strontiumtitanates (BSTs) and lead-zirconate titanates (PZTs).

The dielectric material-containing layers may be formed using methodsappropriate to their materials of composition. Non-limiting examples ofmethods include thermal or plasma oxidation or nitridation methods,chemical vapor deposition methods (including atomic layer chemical vapordeposition methods) and physical vapor deposition methods.

The metal-containing layers could function as electrodes. Non-limitingexamples include certain metals, metal alloys, metal silicides and metalnitrides, as well as doped polysilicon materials (i.e., having a dopantconcentration from about 1×10¹⁸ to about 1×10²² dopant atoms per cubiccentimeter) and polycide (i.e., doped polysilicon/metal silicide stack)materials. The metal-containing layers may be deposited using any ofseveral methods. Non-limiting examples include chemical vapor depositionmethods (also including atomic layer chemical vapor deposition methods)and physical vapor deposition methods. The metal-containing layers couldcomprise a doped polysilicon material (having a thickness typically inthe range 1000 to 1500 Angstrom

The dielectric and metallization stack layer comprises a series ofdielectric passivation layers. Also embedded within the stack layer areinterconnected metallization layers. Components for the pair ofinterconnected metallization layers include, but are not limited tocontact studs, interconnection layers, interconnection studs.

The individual metallization interconnection studs and metallizationinterconnection layers that could be used within the interconnectedmetallization layers may comprise any of several metallization materialsthat are conventional in the semiconductor fabrication art. Non-limitingexamples include certain metals, metal alloys, metal nitrides and metalsilicides. Most common are aluminum metallization materials and coppermetallization materials, either of which often includes a barriermetallization material, as discussed in greater detail below. Types ofmetallization materials may differ as a function of size and locationwithin a semiconductor structure. Smaller and lower-lying metallizationfeatures typically comprise copper containing conductor materials.Larger and upper-lying metallization features typically comprisealuminum containing conductor materials.

The series of dielectric passivation layers may also comprise any ofseveral dielectric materials that are conventional in the semiconductorfabrication art. Included are generally higher dielectric constantdielectric materials having a dielectric constant from 4 to about 20.Non-limiting examples that are included within this group are oxides,nitrides and oxynitrides of silicon. For example, the series ofdielectric layers may also comprise generally lower dielectric constantdielectric materials having a dielectric constant from about 2 to about4. Included but not limiting within this group are hydrogels such assilicon hydrogel, aerogels like silicon Al, or carbon aerogel,silsesquioxane spin-on-glass dielectric materials, fluorinated glassmaterials, organic polymer materials, and other low dielectric constantmaterials such as doped silicon dioxide (e.g., doped with carbon,fluorine), and porous silicon dioxide.

Typically, the dielectric and metallization stack layer comprisesinterconnected metallization layers and discrete metallization layerscomprising at least one of copper metallization materials and aluminummetallization materials. The dielectric and metallization stack layeralso comprises dielectric passivation layers that also comprise at leastone of the generally lower dielectric constant dielectric materialsdisclosed above. The dielectric and metallization stack layer could havean overall thickness from about 1 to about 4 microns. It may comprisefrom about 2 to about 4 discrete horizontal dielectric and metallizationcomponent layers within a stack.

The layers of the stack layer could be patterned to form patterneddielectric and metallization stack layer using methods and materialsthat are conventional in the semiconductor fabrication art, andappropriate to the materials from which are formed the series ofdielectric passivation layers. The dielectric and metallization stacklayer may not be patterned at a location that includes a metallizationfeature located completely therein. The dielectric and metallizationstack layer may be patterned using wet chemical etch methods, dry plasmaetch methods or aggregate methods thereof. Dry plasma etch methods aswell as e-beam etching if the dimension needs to be very small, aregenerally preferred insofar as they provide enhanced sidewall profilecontrol when forming the series of patterned dielectric andmetallization stack layer.

The planarizing layer 11 may comprise any of several opticallytransparent planarizing materials. Non-limiting examples includespin-on-glass planarizing materials and organic polymer planarizingmaterials. The planarizing layer 11 could extend above the optical pipesuch that the planarizing layer 11 would have a thickness sufficient toat least planarize the opening of the optical pipe, thus providing aplanar surface for fabrication of additional structures within the CMOSimage sensor. The planarizing layer could be patterned to form thepatterned planarizing layer.

Optionally, there could be a series of color filter layers 12 locatedupon the patterned planarizing layer 11. The series of color filterlayers, if present, would typically include either the primary colors ofred, green and blue, or the complementary colors of yellow, cyan andmagenta. The series of color filter layers would typically comprise aseries of dyed or pigmented patterned photoresist layers that areintrinsically imaged to form the series of color filter layers.Alternatively, the series of color filter layers may comprise dyed orpigmented organic polymer materials that are otherwise opticallytransparent, but extrinsically imaged while using an appropriate masklayer. Alternative color filter materials may also be used. The filtercould also be filter for a black and white, or IR sensors wherein thefilter cuts off visible and pass IR predominantly.

The spacer layer (13) could be one or more layers made of any materialthat physically, but not optically, separates the stacking layers fromthe micro lens (14). The spacer layer could be formed of a dielectricspacer material or a laminate of dielectric spacer materials, althoughspacer layers formed of conductor materials are also known. Oxides,nitrides and oxynitrides of silicon are commonly used as dielectricspacer materials. Oxides, nitrides and oxynitrides of other elements arenot excluded. The dielectric spacer materials may be deposited usingmethods analogous, equivalent or identical to the methods describedabove. The spacer layer could be formed using a blanket layer depositionand etchback method that provides the spacer layer with thecharacteristic inward pointed shape.

The micro lens (14) may comprise any of several optically transparentlens materials that are known in the art. Non-limiting examples includeoptically transparent inorganic materials, optically transparent organicmaterials and optically transparent composite materials. Most common areoptically transparent organic materials. Typically the lens layers couldbe formed incident to patterning and reflow of an organic polymermaterial that has a glass transition temperature lower than the seriesof color filter layers 12, if present, or the patterned planarizinglayer 11.

In the optical pipe, the high index material in the core could, forexample, be silicon nitride having a refractive index of about 2.0. Thelower index cladding layer material could, for example, be a glass, forexample a material selected from Table II, having a refractive indexabout 1.5.

TABLE II Typical Material Index of Refraction Micro Lens (Polymer) 1.583Spacer 1.512 Color Filter 1.541 Planarization 1.512 PESiN 2.00 PESiO1.46 SiO 1.46In Table II, PESiN refers to plasma enhanced SiN and PESiO refers toplasma enhanced SiO.

Optionally, a micro lens could be located on the optical pipe near theincident electromagnetic radiation beam receiving end of the imagesensor. The function of the micro lens or in more general terms is to bea coupler, i.e., to couple the incident electromagnetic radiation beaminto the optical pipe. If one were to choose a micro lens as the couplerin this embodiment, its distance from the optical pipe would be muchshorter than to the photosensitive element, so the constraints on itscurvature are much less stringent, thereby making it implementable withexisting fabrication technology.

The shape of the optical pipe could be different for differentembodiments. In one configuration, the optical pipe could cylindrical,that is, the diameter of the pipe remains the substantially the samethroughout the length of the optical pipe. In another configuration, theoptical pipe could conical, where the upper diameter of the crosssectional area of the optical pipe could be greater or smaller than thelower diameter of the cross sectional area of the optical pipe. Theterms “upper” and “lower” refer to the ends of the optical pipe locatedcloser to the incident electromagnetic radiation beam receiving andexiting ends of the image sensor. Other shapes include a stack ofconical sections.

Table II lists several different glasses and their refractive indices.These glasses could be used for the manufacture of the optical pipe suchthat refractive index of the core is higher than that of the cladding.The image sensors of the embodiments could be fabricated using differenttransparent glasses having different refractive indices without the useof pigmented color filters.

By nesting optical pipes that function as waveguides and using a microlens coupler as shown in FIG. 2, an array of image sensors could beconfigured to obtain complementary colors having wavelengths ofelectromagnetic radiation separated at a cutoff wavelength in the coreand cladding of each optical pipe of every image sensor. Thecomplementary colors are generally two colors when mixed in the properproportion produce a neutral color (grey, white, or black). Thisconfiguration also enables the capture and guiding of most of theelectromagnetic radiation incident beam impinging on the micro lens tothe photosensitive elements (i.e., photodiodes) located at the lower endof the optical pipe. Two adjacent or substantially adjacent imagesensors with different color complementary separation can providecomplete information to reconstruct a full color scene according toembodiments described herein. This technology of embodiments disclosedherein can further supplant pigment based color reconstruction for imagesensing which suffers from the inefficiency of discarding (throughabsorption) the non selected color for each pixel.

Each physical pixel of a device containing an image sensor of theembodiments disclosed herein would have two outputs representing thecomplementary colors, e.g., blue (complement yellow) designated asoutput type 1 and cyan (complement red) designated as output type 2.These outputs would be arranged as follows:

-   -   1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 . . .    -   2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 . . .    -   1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 . . .    -   . . .    -   . . .

Each physical pixel would have complete luminance information obtainedby combining its two complementary outputs. As a result, the same imagesensor can be used either as a full resolution black and white or fullcolor sensor.

In the embodiments of the image sensors disclosed herein, the fullspectrum of wavelengths of the incident electromagnetic radiation beam(e.g., the full color information of the incident light) could beobtained by the appropriate combination of two adjacent pixels eitherhorizontally or vertically as opposed to 4 pixels for the conventionalBayer pattern.

Depending on minimum transistor sizes, each pixel containing an imagesensor of the embodiments disclosed herein could be as small as 1 micronor less in pitch and yet have sufficient sensitivity. This could openthe way for contact imaging of very small structures such as biologicalsystems.

The embodiments, which include a plurality of embodiments of an imagesensor, as well as methods for fabrication thereof, will be described infurther detail within the context of the following description. Thedescription is further understood within the context of the drawingsdescribed above. The drawings are for illustrative purposes and as suchare not necessarily drawn to scale.

An embodiment comprises a sensor array of two different types of pixels,each different type of pixel having a core of a different diameter suchthat cores have diameters d₁ and d₂ for directing light of differentwavelengths (λ_(B) and λ_(R)). The two cores also serve as photodiodesto capture light of wavelengths λ_(B) and λ_(R). The claddings of thetwo image sensors serve for transmitting the light of wave lengthλ_(w-B) and λ_(w-R). The light of wave length λ_(w-B) and λ_(w-R)transmitted through the cladding is detected by the peripheralphotosensitive elements surrounding the cores. Note that (w) refers tothe wavelength of white light. Signals from the 4 photodiodes (twolocated in the cores and two located in or on the substrate surroundingthe core) in the compound pixel are used to construct color.

The embodiments include a nanostructured photodiode (PD) according tothe embodiments comprise a substrate and an upstanding nanowireprotruding from the substrate. A pn-junction giving an active region todetect light may be present within the structure. The nanowire, a partof the nanowire, or a structure in connection with the nanowire, forms awaveguide directing and detecting at least a portion of the light thatimpinges on the device. In addition the waveguide doubles up as spectralfilter that enables the determination of the color range of theimpinging light.

The waveguiding properties of the optical pipe of the embodiments can beimproved in different ways. The waveguide core has a first effectiverefractive index, n₁ (also referred as n_(w) below), and the material inthe cladding surrounding at least a portion of the waveguide has asecond effective refractive index, n₂ (also referred as n_(c) below),and by assuring that the first refractive index is larger than thesecond refractive index, n₁>n₂, good wave-guiding properties areprovided to the optical pipe. The waveguiding properties may be furtherimproved by introducing optically active cladding layers on thewaveguide core. The nanowire core is used as a waveguide, and also as ananostructured PD which may also be an active capacitor. Thenanostructured PD according to the embodiments is well suited for massproduction, and the method described is scaleable for industrial use.

The nanowire technology offers possibilities in choices of materials andmaterial combinations not possible in conventional bulk layertechniques. This is utilised in the nanostructured PD according to theembodiments to provide PDs detecting light in well defined wavelengthregions not possible by conventional technique, for example blue, cyanor white. The design according to the embodiments allows for inclusionsof heterostructures as well as areas of different doping within thenanowire, facilitating optimization of electrical and/or opticalproperties.

A nanostructured PD according to the embodiments comprises of anupstanding nanowire. For the purpose of this application an upstandingnanowire should be interpreted as a nanowire protruding from thesubstrate in some angle, the upstanding nanowire for example being grownfrom the substrate, preferably by as vapor-liquid-solid (VLS) grownnanowires. The angle with the substrate will typically be a result ofthe materials in the substrate and the nanowire, the surface of thesubstrate and growth conditions. By controlling these parameters it ispossible to produce nanowires pointing in only one direction, forexample vertical, or in a limited set of directions. For examplenanowires and substrates of zinc-blende and diamond semiconductorscomposed of elements from columns III, V and IV of the periodic table,such nanowires can be grown in the [111] directions and then be grown inthe normal direction to any {111} substrate surface. Other directionsgiven as the angle between normal to the surface and the axial directionof the nanowire include 70.53° {111}, 54.73° {100}, and 35.27° and 90°,both to {110}. Thus the nanowires define one, or a limited set, ofdirections.

According to the embodiments, a part of the nanowire or structure formedfrom the nanowire is used as a waveguide directing and confining atleast a portion of the light impinging on the nanostructured PD in adirection given by the upstanding nanowire. The ideal waveguidingnanostructured PD structure includes a high refractive index core withone or more surrounding cladding with refractive indices less than thatof the core. The structure is either circular symmetrical or close tobeing circular symmetrical. Light waveguiding in circular symmetricalstructures are well know for fiber-optic applications and many parallelscan be made to the area of rare-earth-doped fiber optic devices.However, one difference is that fiber amplifier are optically pumped toenhance the light guided through them while the described nanostructuredPD can be seen as an efficient light to electricity converter. One wellknown figure of merit is the so called Numerical Aperture, NA. The NAdetermines the angle of light captured by the waveguide. The NA andangle of captured light is an important parameter in the optimization ofa new PD structure.

For a PD operating in IR and above IR, using GaAs is good, but for a PDoperating in the visible light region, silicon would be preferable. Forexample to create circuits, Si and doped Si materials are preferable.Similarly, for a PD working in the visible range of light, one wouldprefer to use Si.

In one embodiment, the typical values of the refractive indexes forIII-V semiconductor core material are in the range from 2.5 to 5.5 whencombined with glass type of cladding material (such as SiO₂ or Si₃N₄)having refractive indexes ranging from 1.4 to 2.3. A larger angle ofcapture means light impinging at larger angles can be coupled into thewaveguide for better capture efficiency.

One consideration in the optimization of light capture is to provide acoupler into the nanowire structure to optimize light capture into thestructure. In general, it would be preferred to have the NA be highestwhere the light collection takes place. This would maximize the lightcaptured and guided into the PD.

A nanostructured PD according to the embodiments is schematicallyillustrated in FIG. 2 and comprises a substrate and a nanowireepitaxially grown from the substrate in an defined angle θ. A portion ofor all of the nanowire could be arranged to act as a waveguiding portiondirecting at least a portion of the impinging light in a direction givenby the elongated direction of the nanowire, and will be referred to as awaveguide. In one possible implementation, a pn-junction necessary forthe diode functionality is formed by varying the doping of the wirealong its length while it is growing. Two contact could be provided onthe nanowire for example one on top or in a wrapping configuration onthe circumferential outer surface (depicted) and the other contact couldbe provided in the substrate. The substrate and part of the upstandingstructure may be covered by a cover layer, for example as a thin film asillustrated or as material filling the space surrounding thenanostructured PD.

The nanowire typically has a diameter in the order of 50 nm to 500 nm,The length of the nanowire is typically and preferably in the order of 1to 10 μm. The pn-junction results in an active region arranged in thenanowire. Impinging photons in the nanowire are converted to electronhole pairs and in one implementation are subsequently separated by theelectric fields generated by the PN junction along the length of thenanowire. The materials of the different members of the nanostructuredPD are chosen so that the nanowire will have good waveguiding propertiesvis-a-vis the surrounding materials, i.e. the refractive index of thematerial in the nanowire should preferably be larger than the refractiveindices of the surrounding materials.

In addition, the nanowire may be provided with one or more layers. Afirst layer, may be introduced to improve the surface properties (i.e.,reduce charge leakage) of the nanowire. Further layers, for example anoptical layer may be introduced specifically to improve the waveguidingproperties of the nanowire, in manners similar to what is wellestablished in the area of fiber optics. The optical layer typically hasa refractive index in between the refractive index of the nanowire andthe surrounding cladding region material. Alternatively the intermediatelayer has a graded refractive index, which has been shown to improvelight transmission in certain cases. If an optical layer is utilised therefractive index of the nanowire, n_(w), should define an effectiverefractive index for both the nanowire and the layers.

The ability to grow nanowires with well defined diameters, as describedabove and exemplified below, is in one embodiment utilised to optimizethe waveguiding properties of the nanowire or at least the waveguidewith regards to the wavelength of the light confined and converted bythe nanostructured PD. In the embodiment, the diameter of the nanowireis chosen so as to have a favorable correspondence to the wavelength ofthe desired light. Preferably the dimensions of the nanowire are suchthat a uniform optical cavity, optimized for the specific wavelength ofthe produced light, is provided along the nanowire. The core nanowiremust be sufficiently wide to capture the desired light. A rule of thumbwould be that diameter must be larger than λ/2n_(w), wherein λ is thewavelength of the desired light and n_(w) is the refractive index of thenanowire. As an example a diameter of about 60 nm may be appropriate toconfine blue light only and one 80 nm may be appropriate for to confineboth blue and green light only in a silicon nanowire.

In the infra-red and near infra-red, a diameter above 100 nm would besufficient. An approximate preferred upper limit for the diameter of thenanowire is given by the growth constrains, and is in the order of 500nm. The length of the nanowire is typically and preferably in the orderof 1-10 μm, providing enough volume for the light conversion region

A reflective layer is in one embodiment, provided on the substrate andextending under the wire. The purpose of the reflective layer is toreflect light that is guided by the wire but has not been absorbed andconverted to carriers in the nanostructured PD. The reflective layer ispreferably provided in the form of a multilayered structure comprisingrepeated layers of silicates for example, or as a metal film. If thediameter of the nanowire is sufficiently smaller than the wavelength ofthe light a large fraction of the directed light mode will extendoutside the waveguide, enabling efficient reflection by a reflectivelayer surrounding the narrow the nanowire waveguide

An alternative approach to getting a reflection in the lower end of thewaveguide core is to arrange a reflective layer in the substrateunderneath the nanowire. Yet another alternative is to introducereflective means within the waveguide. Such reflective means can be amultilayered structure provided during the growth process of thenanowire, the multilayered structure comprising repeated layers of forexample SiN_(x)/SiO_(x) (dielectric).

The previous depicted cylindrical volume element which is achievablewith the referred methods of growing nanowires, should be seen as anexemplary shape. Other geometries that are plausible include, but is notlimited to a cylindrical bulb with a dome-shaped top, aspherical/ellipsoidal, and pyramidal.

Preferably, the color response of a color light sensor is closelymatched to the color response of the human eye. In one embodiment, thefirst step to optimize the diameter of a nanowire photodetector is toalign the response of the nanowire of a desired wavelength with thecorresponding response curves of the human eye using computersimulation. For example, the response of a nanowire with a desired blueand green response may be aligned to the blue and green response curvesof the human eye. By closely matching the response of the photodiodes ofthe color light sensor to the response of the human eye, problems suchas matamerism (when tow color samples appear to match under a particularlight source and then do not match under a different light source) andloss of color fidelity under varying light illumination can be reducedor essentially eliminated.

One embodiment includes two different nanowire sensors or pixels.Preferably, the first nanowire sensor includes a light pipe with a coreconfigured to channel blue light. Preferably, the core of the firstnanowire sensor is surrounded with a cladding configured to channellight of the complementary color of the core. In the case of a corechanneling blue light, the cladding preferably channels yellow light.Preferably, the second nanowire sensor includes a light pipe with a coreconfigured to channel cyan light. Preferably, the core of the secondnanowire sensor is surrounded with a cladding configured to channellight of the complementary color to the second core. In the case of acore channeling cyan light, the cladding preferably channels red light.The degree to which a linear combination of the spectral response of theblue and cyan nanowires and their complementary responses fit the eyeresponse curves determines the color reproduction capability of theimage sensor.

Numerous standard response curves of the human eye are known. In someembodiments, the Smith-Pokorny human eye response curves (shown in FIG.5) could be used for the determination of an error difference betweenthe spectral response of the image sensor of the claimed invention andthe Smith-Pokorny human eye response curves. The Smith-Pokorny human eyeresponse curves are linear combinations of the Commission Internationaled'Eclairage (CIE) eye response curves. The Smith-Pokorny human eyeresponse curves are not only standard, but have the added benefit ofhaving positive response at all points of the visible spectrum. Otherstandard response curves, however, may be used. Other standard responsecurves include, but are not limited to, CIE RGB, CIE, XYZ, CIE Lab, CIEUVW, and CIE Luv. In the CIE Luv system, u and v are chromaticitycoordinates (or chrominance) and L is the luminance.

In one embodiment, the optimal diameters of the cores of the nanowiresensors are determined by computer simulation. In this embodiment, twodifferent nanowire sensors are used. The diameters of the nanowire coresof the first and second nanowire sensors are preselected along with thematerials of the nanowire cores and claddings. Based on the materialproperties of the cores and the claddings and any optional features ofthe sensor (e.g. reflective layer surrounding the light pipe, reflectivelayer on the substrate, etc.), a simulation is run to determine thespectral characteristics of the nanowire sensors. Preferably, thesimulation includes the effect of crosstalk. The spectral response ofthe nanowire sensors are then compared to standard spectral responsecurves to determine the difference, or error between the nanowiresensors and the standard spectral response curves.

In one aspect, the computer simulation was run with FullWAVE™ softwarefrom RSOFT Design Group. FullWAVE™ is a Finite Difference Time Domain(FDTD) Maxwell's Equations solver. Results of this aspect areillustrated in FIGS. 7 and 8.

FIG. 7 illustrates the results of a simulation of the absorption of a 60nm nanowire and a 80 nm nanowire. As can be seen from FIG. 7, in thecase of Si, the 60 nm nanowire primarily absorbs blue light(approximately 450-500 nm), allowing light of higher wavelengths to leakout of the nanowire. The 80 nm nanowire absorbs primarily blue light(approximately 450-500 nm) and green light (approximately 500-570 nm),allowing light of higher wavelengths to leak out of the nanowire. Thus,the 60 nm nanowire primarily retains only blue light while allowing thecompliment, yellow light, to leak out. The 80 nm nanowire primarilyretains only blue and green (cyan) light while allowing its compliment,red light, to leak out. Note, both the 60 nm nanowire and the 80 nmnanowire absorb some higher (orange/red) wavelength light. This is dueto spectral crosstalk as discussed above.

FIG. 8 illustrates the results of a simulation of the absorption of thesubstrates of a 60 nm nanowire device and a 80 nm nanowire device. Thatis, FIG. 8 illustrates the results of the light that leaks out of the 60nm nanowire and 80 nanowire illustrated in FIG. 7. As can be seen inFIG. 8, the absorption is low for both the 60 nm nanowire substrate andthe 80 nm nanowire substrate. That is, essentially all of the light thatleaks out of the 60 nm nanowire and 80 nm nanowire reaches thesubstrate. Note, both the 60 nm nanowire substrate and the 80 nmnanowire substrate absorb some lower (blue/green) wavelength light. Thisis due to spectral crosstalk as discussed above.

In one embodiment, the standard spectral response curves used areSmith-Pokorny eye response spectral curves (illustrated in FIG. 5). Inthe following example (illustrated in FIG. 3), the first nanowire sensorinclude a blue core with a complementary yellow cladding. The secondnanowire sensor include a cyan core with a complementary red cladding.If Rsp, Gsp, and Bsp are the Smith-Pokorny eye response spectral curvesfor red, green, and blue respectively, the error can be calculated fromthe following equations:Rsp=Ayr*Ynw+Abr*Bnw+Arr*Rnw+Acr*Cnw,Gsp=Ayg*Ynw+Abg*Bnw+Arg*Rnw+Acg*Cnw,Bsp=Ayb*Ynw+Abb*Bnw+Arb*Rnw+Acb*Cnw,

where Ynw and Bnw are the spectral responses of the first nanowire, Rnwand Cnw are the spectral responses of the second nanowire, and Ayr, Abr,Arr, Acr, Ayg, Abg, Arg, Acg, Ayb, Abb, Arb, Acb are constants. Thevalue of the constants Axx are determined such that the above equationsare satisfied with the least error. The spectral error of the device canthen be determined by taking a least square fit of the error between thebest fit spectral response curves of the nanowire sensor devices and theSmith-Pokorny eye response spectral curves. In alternative embodiments,the spectral error of the device can be determined by other regressionor curve fitting techniques, such as least square parabola and leastsquare m^(th) degree polynomial. After the spectral error of the deviceis calculated, new diameters may be selected for the first and secondnanowire devices and the process repeated until the above equations aresatisfied with the least error, thereby identifying the nanowirediameters resulting to the lowest total error from the standardSmith-Pokorny eye response spectral curves.

In alternative embodiments, rather than a simulation, actual devices arefabricated and the actual spectral responses measured. The spectralerrors between the actual device and a standard spectral response curveare determined. In this way, the diameter of the nanowire sensor devicescan be optimized with actual nanowire sensor devices.

Other embodiments relate to scene reconstruction based on digitizedresponses taken with nanowire sensor devices. Each pair of pixels hascomplete luminance information obtained by combining its twocomplementary outputs. As a result, the same image sensor can be usedeither as a full resolution black and white or full color sensor.Further, the color reconstruction could be done to obtain full colorinformation by the appropriate combination of two adjacent pixels. Thepixels may be either horizontally or vertically adjacent. Further,because all the information can be obtained with two adjacent pixels,the reconstruction method of the present embodiment is more efficientand may be faster than the 4 pixel method required by the Bayer patternof convention image sensors.

In a first scene reconstruction method embodiment, digitized responsesare received from a sensor array comprising alternating pixels ofnanowire photodiodes. In the following example, the reconstructionmethod is based on the photodiode sensor array illustrated in FIG. 3. InFIG. 3, the array has been illustrated as a 2×2 matrix. However, thefour nanowire photodiodes may be configured in the same row. Indeed, forthe following explanation of the method of this embodiment, it will beassumed that the four nanowire photodiodes are in the same row.

In this embodiment, the first and third nanowire photodiodes (pixels 1and 3) have a blue core and a yellow cladding. The second and fourthnanowire photodiodes (pixels 2 and 4) have a cyan core and a redcladding. In this embodiment, the scene is reconstructed by taking thedigitized responses of two adjacent pixels at a time and transformingthe digitized responses of the two adjacent pixels to determine the red,green, and blue color of the scene. The transformation is performed withthe use of color matching functions, the use of which are well known inthe art. Color matching functions are a numerical description of thechromatic response of the observer. By applying the appropriate colormatching function, the yellow, blue, cyan, and red outputs of adjacentpixels can be mathematically transformed to the red, blue and greenresponse of the standard observer.

In this embodiment, the transformation is performed by stepping across arow one pixel at a time. That is, first the color data from pixels 1 and2 are transformed, then 2 and 3, then 3 and 4, and so on until the endof the row is reached. After transformation of the first row iscompleted, the next row is transformed in a similar manner and so on,until the entire scene or image is reconstructed.

Because a single row of pixels can be transformed by stepping across therow, there is no need to buffer an entire row of pixels as is necessaryto transform conventional Bayer configured color sensors (discussedabove). Thus, the present embodiment can be transformed more quickly andmore efficiently than a conventional Bayer configured color sensor.

The first scene reconstruction method embodiment can be performed withthe following equations for the first pair of pixels (pixels 1 and 2):R1=Ayr*Y1+Abr*B1+Arr*R2+Acr*C2,G1=Ayg*Y1+Abg*B1+Arg*R2+Acg*C2,B1=Ayb*Y1+Abb*B1+Arb*R2+Acb*C2,where Y1 and B1 are spectral responses of the first yellow/blue nanowirephotodiode device (pixel 1), R2 and C2 are spectral responses of thesecond red/cyan nanowire photodiode device (pixel 2), and Ayr, Abr, Arr,Acr, Ayg, Abg, Arg, Acg, Ayb, Abb, Arb, Acb are constants. For thesecond pair of pixels (pixels 2 and 3), the following equations may beused:R2=Ayr*Y3+Abr*B3+Arr*R2+Acr*C2,G2=Ayg*Y3+Abg*B3+Arg*R2+Acg*C2,B2=Ayb*Y3+Abb*B3+Arb*R2+Acb*C2,Where Y3 and B3 are spectral responses of the third yellow/blue nanowirephotodiode device (pixel 3), R2 and C2 are the spectral response of thesecond red/cyan nanowire photodiode device (pixel 2), and Ayr, Abr, Arr,Acr, Ayg, Abg, Arg, Acg, Ayb, Abb, Arb, Acb are constants. The remainingpixels in the sensor array are transformed by stepping across the rowone pixel at a time and solving equations as above.

In a second scene reconstruction method embodiment, digitized responsesare also received from a sensor array comprising alternating pixels ofnanowire photodiodes. In this embodiment (array in FIG. 3), the firstand third nanowire photodiodes (pixels 1 and 3) have a blue core and ayellow cladding. The second and fourth nanowire photodiodes (pixels 2and 4) have a cyan core and a red cladding. In this embodiment, thescene is reconstructed by taking the digitized responses of two adjacentpixels at a time and transforming the digitized responses to determinethe luminance and the chrominance of the scene. In this embodiment, thetransformation is performed by stepping across a row two pixels at atime. That is, first pixels 1 and 2 are transformed, then 3 and 4, then5 and 6, and so on until the end of the row is reached. After the firstrow is completed, the next row is transformed in a similar manner.Because, as in the first scene reconstruction method embodiment, asingle row pixels can be transformed by stepping across the row, thereis no need to buffer an entire row as is necessary with conventionalBayer configured color sensors. Thus, the second scene reconstructionmethod embodiment also can be transformed more quickly and moreefficiently than a conventional Bayer configured color sensor.

The transformation via the second scene reconstruction method embodimentcan be performed with the equations below, illustrated for the firstpair of pixels (pixels 1 and 2). In this example, the transformation isperformed using the CIE Luv transformation which include a luminancevalue (L) and two chromance coordinates (u, v) to fully describe thecolor.Luminance1=Ly*Y1+Lb*B1,Luminance2=Lr**R2+Lc*C2,Chrominance1=Ayu*Y1+Abu*B1+Aru*R2+Acu*C2,Chrominance2=A*Y1+Abv*B1+Arv*R2+Acv*C2,Where Y1, B1 and R2, C2 are the spectral responses of the first andsecond nanowire photodiode devices, respectively, and Ly, Lb, Lr, Lc,Ayu, Ayv, Abu, Abv, Aru, Arv, Acu, and Acv are constants. The remainingpixels in the array are transformed in a similar manner.In the above scene reconstruction methods, the data is transformed onerow at a time. In alternative embodiments, the nanowire color sensor isconfigured so that more than one row can be transformed at the sametime. This may be accomplished, for example, with the addition ofprocessing circuitry. In still another embodiment, the transformationmay be performed in an interlaced fashion. In an alternative embodiment,the data can be subsampled. Because the human visual system is lesssensitive to the position and motion of color than the luminance,bandwidth can be optimized by storing more luminance detail than colordetail. Subsampling can be done, for example, with 4:2:2 subsampling.With 4:2:2 subsampling, the two chrominance components are sampled athalf the sample rate of luminance. Thus, the horizontal chrominanceresolution is halved. This reduces the bandwidth of a video signal byone-third with little to no visual difference. The output data stream inthe 4:2:2 format is of the form:

Luminance1, Chrominance1, Luminance2, Chrominance2, . . . . Othersubsampling formats include, but are not limited to, 4:2:1, 4:1:1, and4:2:0.

FIG. 4 is a schematic illustration of a sensor according to anembodiment. Each physical pixel of a device containing an image sensorof the embodiments disclosed herein would have two outputs representingthe complementary colors, e.g., cyan, red (C, R) designated as outputtype 1 or yellow, blue (Y, B) designated as output type 2 as shown inFIG. 4. These four outputs of two pixels can be resolved to reconstructa full color scene of an image viewed by a device containing the imagesensors of the embodiments described herein.

Another embodiment relates to a computer readable medium comprisingcomputer executable instructions for simulating nanowire photodiode(pixel) devices. With this embodiment, the diameters of nanowires of thenanowire photodiodes (pixels) can be optimized to minimize the errordifference in spectral response between the nanowire photodiodes and thespectral response of the human eye. The spectral response of the humaneye may be represented with standard eye response curves such as the CIEcurves or the Smith-Pokorny eye response spectral curves. The minimum orleast error difference may be determined with the use of a least squaresanalysis. The simulation may take into account the effect of crosstalk.

In one embodiment, the cladding could be absent such that thecomplementary color is detected by the photodiode on the substrate.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of diagrams, flowcharts, and/orexamples. Insofar as such diagrams, flowcharts, and/or examples containone or more functions and/or operations, it will be understood by thosewithin the art that each function and/or operation within such diagrams,flowcharts, or examples can be implemented, individually and/orcollectively, by a wide range of hardware, software, firmware, orvirtually any combination thereof. In one embodiment, several portionsof the subject matter described herein may be implemented viaApplication Specific Integrated Circuits (ASICs), Field ProgrammableGate Arrays (FPGAs), digital signal processors (DSPs), or otherintegrated formats. However, those skilled in the art will recognizethat some aspects of the embodiments disclosed herein, in whole or inpart, can be equivalently implemented in integrated circuits, as one ormore computer programs running on one or more computers (e.g., as one ormore programs running on one or more computer systems), as one or moreprograms running on one or more processors (e.g., as one or moreprograms running on one or more microprocessors), as firmware, or asvirtually any combination thereof, and that designing the circuitryand/or writing the code for the software and or firmware would be wellwithin the skill of one of skill in the art in light of this disclosure.In addition, those skilled in the art will appreciate that themechanisms of the subject matter described herein are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the subject matter described herein appliesregardless of the particular type of signal bearing medium used toactually carry out the distribution. Examples of a signal bearing mediuminclude, but are not limited to, the following: a recordable type mediumsuch as a floppy disk, a hard disk drive, a Compact Disc (CD), a DigitalVideo Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein can beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops and control motors (e.g., feedback forsensing position and/or velocity; control motors for moving and/oradjusting components and/or quantities). A typical data processingsystem may be implemented utilizing any suitable commercially availablecomponents, such as those typically found in datacomputing/communication and/or network computing/communication systems.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable,” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to optical coupling to permit transmission of optical light,for example via an optical pipe or fiber, physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

All references, including but not limited to patents, patentapplications, and non-patent literature are hereby incorporated byreference herein in their entirety.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A method comprising: providing or obtaining atleast a first nanowire device comprising at least a first pixel and asecond pixel, wherein the first pixel comprises a first nanowirecomprising a first predetermined material and a first diameter, thefirst pixel configured to detect light of a first predeterminedwavelength, and the second pixel comprises a second nanowire comprisinga second predetermined material and a second diameter, the second pixelconfigured to detect light of a second predetermined wavelength;determining a first error difference between a first spectral responseof the first nanowire to the light of the first predetermined wavelengthand one or more standard spectral response curves; determining a seconderror difference between a second spectral response of the secondnanowire to the light of the second predetermined wavelength and the oneor more standard spectral response curves; and determining a total errordifference of the first nanowire device at least from the first andsecond error differences; wherein at least one of the firstpredetermined wavelength and the second predetermined wavelength is aninfrared wavelength.
 2. The method of claim 1, further comprising:determining the first and second diameters that produce the a leastvalue of the total error difference.
 3. The method of claim 1, whereinthe standard spectral response curves include Smith-Pokorny eye responsespectral curves.
 4. The method of claim 1, wherein the standard spectralresponse curves include CIE standard observer curves.
 5. The method ofclaim 1, wherein the total least error difference is determined with aleast squares analysis.
 6. The method of claim 1, wherein at least oneof the first predetermined material and the second predeterminedmaterial is GaAs.
 7. The method of claim 1, further comprising filteringlight through a filter that cuts off visible light and passes infraredlight.
 8. The method of claim 1, wherein the first nanowire devicecomprises an optical pipe comprising a core and a cladding, wherein thecore is configured to transmit light with wavelengths up to the firstpredetermined wavelength.
 9. The method of claim 1, wherein the firstnanowire has a diameter of above 100 nm.
 10. The method of claim 1,further comprising fabricating a sensor array having a plurality offirst and second pixels.
 11. The method of claim 10, wherein the sensorarray comprises rows and columns of alternating first and second pixels.12. A non-transitory computer readable medium comprising computerexecutable instructions for the method of claim
 1. 13. The method ofclaim 1, further comprising: providing a plurality of additionalnanowire devices, each of the additional nanowire devices comprising atleast an additional first pixel and an additional second pixel, whereineach of the additional first pixels comprises an additional firstnanowire comprising the first predetermined material but having adifferent diameter from each of the other additional first nanowires andfrom the first nanowire and each of the additional second pixelscomprise an additional second nanowire comprising the secondpredetermined material but having a different diameter from each othersecond additional nanowires and from the second nanowire; determiningtotal error differences of the additional nanowire devices.
 14. A methodcomprising: receiving digitized responses of an array of nanowirephotodiode devices, the array comprising an alternating plurality offirst nanowire photodiode devices and second nanowire photodiodedevices, the first nanowire photodiode devices configured to detectlight of a first wavelength and the second nanowire photodiode devicesconfigured to detect light of a second wavelength; and transforming thedigitized responses by stepping across a row of alternating first andsecond nanowire photodiode devices, wherein at least one of the firstwavelength and the second wavelength is an infrared wavelength.
 15. Themethod of claim 14, wherein stepping across the row is performed onenanowire photodiode device at a time.
 16. The method of claim 14,wherein the first nanowire photodiode devices and second nanowirephotodiode devices comprise GaAs.
 17. The method of claim 14, whereinstepping across a row is performed a pair of nanodiodes devices at atime.
 18. The method of claim 17, further comprising using a 4:2:2subsampling.
 19. A non-transitory computer readable medium comprisingcomputer executable instructions for the method of claim
 14. 20. Adevice comprising at least a first pixel and a second pixel, wherein thefirst pixel comprises a first nanowire comprising a first predeterminedmaterial and a first predetermined diameter, the first pixel configuredto detect light of a first predetermined wavelength and the second pixelcomprises a second nanowire comprising a second predetermined materialand a second predetermined diameter, the second pixel configured todetect light of a second predetermined wavelength, wherein the firstnanowire and the second nanowire have diameters which were determined toproduce the least total error difference between spectral responses ofthe first and second pixels with standard spectral response curves;wherein at least one of the first predetermined wavelength and thesecond predetermined wavelength is an infrared wavelength.
 21. Thedevice of claim 20, wherein the device is an optical sensor.
 22. Thedevice of claim 20, wherein at least one of the first predeterminedmaterial and the second predetermined material is GaAs.
 23. The deviceof claim 20, wherein the least total error difference is determined witha least squares analysis.
 24. The device of claim 20, wherein the firstpixel comprises a first light pipe comprising the first nanowire and afirst cladding surrounding the first nanowire and the second pixelcomprises a second light pipe comprising the second nanowire and asecond cladding surrounding the first nanowire.
 25. The device of claim24, wherein the first pixel further comprises a reflective surfacesurrounding the first light pipe and the second pixel further comprisesa reflective surface surrounding the second light pipe.
 26. The deviceof claim 24, wherein the first pixel comprises a first substrate and afirst photodiode in the first substrate, the second pixel comprises asecond substrate and a second photodiode in the second substrate.